I don't know why or what's wrong with me, but I can not run long distance. I did cross country and track for 3 years in high school, and my times never improved. At all. I just recently started crossfit and I realized I just cannot run. Today's workout was only a combined total of 1.25 miles and even the first 400 meters I was dying. Everyone says well just run more and you'll get better but I don't seem to be. I need suggestions, or maybe even some kind of diagnosis as to why running is such a problem for me.